Are there any halachic issues with a tankless water heater in a Chabad house (or home) for Yom Tov?


Tankless “instant-on” units may not be used on Yom Tov. With regards to storage tank (boiler) hot water supply units, there are different opinions, as explained below.



Storage Tank – These units are either gas or electric powered. The water is heated in an insulated tank until it reaches a pre-set temperature, and the water is stored until needed. When the faucet is opened, some of the heated water flows out to the faucet, and new cold water enters the tank to replace it. The introduction of cold-water results in a temperature drop. When this is detected by the thermostat, the heater is activated to reheat the water. In such heaters, turning on the hot water faucet ultimately causes the thermostat to activate the heater.

If the unit is powered by a gas heater, and it is ignited by a constantly burning pilot flame, as is the case with older gas units, one may use it on Yom Tov, for it is permissible to light a fire from a pre-existing flame on Yom Tov.

If the unit is powered by an electric heater, or is equipped with a gas heater fired by electric ignition (which is more common with newer gas units), then there is a difference of opinion.

Some Poskim permit their use on the basis of a a number of complex Halachic principles which, taken all together, provide basis for its use on Yom Tov. These principles in a nutshell: First, since the heater constantly cycles on and off, it is not certain that opening the hot water faucet will activate the heater, for it may have already been operating at just that moment. Furthermore, the objective when opening the faucet is merely to access the already heated water, and the heater’s activation is an unintended consequence. Finally, even if the heater is in fact activated by opening the hot water faucet, the process is not immediate; it only takes place after the thermostat has detected the temperature drop. The heater’s activation is therefore treated as an indirect result (“Grama”) of turning on the faucet. Although each of these factors alone is not necessarily sufficient to permit the unit’s use, taken together, they form a sufficient basis to be lenient. [It is important to note that these factors are insufficient for allowing the unit’s use on Shabbos.]

There is another issue which needs to be addressed. The introduction of cold water into the unit – whether electric or gas – would itself seem problematic, because even without the heater powering on, the already heated water inside the unit will warm the new water to the temperature of Yad Soledes (commonly accepted as 42-45 degrees Celsius), which is tantamount to cooking.  Although it is permissible to cook on Yom Tov for the purposes of eating and drinking on Yom Tov, the newly-cooked water might not be used until after Yom Tov! The Shmiras Shabbos Kehilchasa answers that since the already heated water cannot be obtained from the unit without allowing new water to enter, the new water is regarded as having been heated for the sake of the present moment, and not for the sake of the future.

Based on the above, many are accustomed to using such heaters on Yom Tov, and they have upon whom to rely. Other Poskim recommend that such hot water units not be used on Yom-Tov, and not to rely on the above leniencies.

Tankless (“Instant-On”) – Rather than storing water, tankless water units use heating coils to heat the water each time the faucet is turned on. Opening the hot water faucet automatically causes the heater to instantly turn on. This is forbidden both in the case of an electric heater, as well as in the case of a gas heater lit by electric ignition, or ventilated with an electric fan. Similarly, closing the faucet is forbidden as well, for it automatically causes the electric heater and fan to instantly turn off.

None of the three alleviating factors mentioned above apply to a tankless heater. First, it is absolutely certain that opening the hot water faucet will activate the heater. Second, the heater’s activation is surely intended, because one’s objective in opening the faucet is to heat the cold water passing through the tankless unit. Finally, the heater’s activation is instant.

What about a gas heater which does not have a fan? If ignited by a pilot flame (as opposed to electric ignition), it would be permissible to open the faucet and activate the heater, for it is permissible to light a fire from a pre-existing flame on Yom Tov. However, one would not be able to close the faucet, as doing so would instantly extinguish the flames of the gas heater, which is forbidden even on Yom Tov. This problem effectively rules out the use of even such a heater on Yom Tov.




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